1. Field of Invention
The present invention relates to a universal joint.
2. Prior Art
Universal joints are commonly used to transmit rotational motion between two shafts, both being coplanar; they commonly consist of two shafts, each having a yoke, mounted rotatably and perpendicularly to a centerpiece. The universal joint thus uses two connections, each being a hinge joint.
Gimbal joints are commonly used to allow certain degrees of motion freedom, having one side stationary and the other movable; they commonly consist of 3 concentric rings of different diameter, mounted rotatably and perpendicularly. The intermediate ring functions as the centerpiece being connected to the inner and outer ring. Thus the gimbal joint also uses two connections, each being a hinge joint.
Both, the universal joint and gimbal joint, are closely related, such that the improvements of this patent are relevant for both structures. The use of the term universal joint from hereon should be viewed as inclusive in regard to the gimbal joint.
The universal joint commonly uses bearings such as pin bearings, roller bearings, ball bearings, or friction bearings to facilitate rotation. All these can be made using different degrees of tolerance. However, greater precision usually requires greater expense. The number of connections in a complex joint is negatively correlated to the degree of precision, each connection reducing precision. A center-less universal joint would reduce the number of connections to a single one, a direct interface between the two yokes.
U.S. Pat. No. 7,084,337 to Schroeder (2003) uses a universal joint to allow motion of a musical instrument while restricting rotation of such instrument around its longitudinal axis. The degree of precision while moving the instrument is highly important and it would thus be beneficial to have a universal joint of ultra tight tolerance, yet simple enough to allow inexpensive manufacturing.
Since the musical instrument interfaces with a support, this being a single connection, it would be of advantage to have a two part universal joint that can be easily engaged and disengaged, wherein one part would be attached to the support and the other to the instrument. Engaging the instrument-support interface would engage the universal joint interface. This engagement process should be easy; the instrument should align itself with the support such that the rotational axes of the universal joint are aligned perpendicularly. In the same manner the disengagement should be made simple allowing the player to easily release the instrument from the support. A further requirement of the joint in combination with a musical instrument would be safety; all protruding parts should have smooth surfaces. This is especially important if the player is a child. The weight of the instrument in addition to the forces applied by the player further require the joint to be durable.
U.S. Pat. No. 4,968,173 to Fujita (1990) shows a universal joint that can be disengaged as well as engaged by sliding a first yoke onto a spherical center piece connected to a second yoke. Fitting the spherical section on the yoke to the spherical center piece requires high precision to achieve smooth operation. This solution would thus not combine ultra tight tolerance and low cost.
The parts of most universal joints are not easily assembled or disassembled; thus these joints are often used as modules fitted with additional connectors to serve applications which require an easy interface for rapid connection and release.
Awnings use universal joints to allow the user to operate the crank shaft from different angles. The interface between crank and awning is often quite difficult to establish having to align the crank shaft to be collinear with the shaft of the awning's universal joint; in addition the rotational orientation of the crank shaft has to match that of the universal joint to allow the usual snap-in connection. A more usable system would be preferable.
Screwdrivers are usually used applying force against a screw while rotating the screw with the screw driver. Both screw and driver are designed to be used with collinear rotational axes. Universal joint modules can be used to allow non collinear operation, but they add to the instability of the system due to the increased number of non-weld connections. It would be beneficial to have an improved interface between screw and screwdriver that integrates the functionality of a universal joint. While wobble hex bits allow non-collinear operation, the design of the interface between driver and screw is biased towards collinear operation; thus this design is not a universal joint.